Systems and methods related to linear and efficient broadband power amplifiers

ABSTRACT

Systems and methods related to linear and efficient broadband power amplifiers. A power amplifier (PA) system can include an input circuit configured to receive a radio-frequency (RF) signal and split the RF signal into a first portion and a second portion. The PA system can further include a Doherty amplifier circuit including a carrier amplification path coupled to the input circuit to receive the first portion and a peaking amplification path coupled to the input circuit to receive the second portion. The PA system can further include an output circuit coupled to the Doherty amplifier circuit. The output circuit can include a balance to unbalance (BALUN) circuit configured to combine outputs of the carrier amplification path and the peaking amplification path to yield an amplified RF signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Application No.61/992,842 filed May 13, 2014, entitled SYSTEMS AND METHODS RELATED TOLINEAR AND EFFICIENT BROADBAND POWER AMPLIFIERS, the disclosure of whichis hereby expressly incorporated by reference herein in its entirety.

BACKGROUND

1. Field

The present disclosure generally relates to radio-frequency (RF) poweramplifiers (PAs).

2. Description of the Related Art

Traditionally, it has been widely believed that the Doherty PA was notsuitable for linear PA applications in handsets due to the size,complexity, and non-linear behavior. In fact, in base stationapplications, predistortion linearizers are typically used with DohertyPAs to meet linearity requirements. As described herein, issues such assize, complexity, and linearity associated with Doherty PAs can beaddressed appropriately.

SUMMARY

In accordance with some implementations, the present disclosure relatesto a power amplifier (PA) system including an input circuit configuredto receive a radio-frequency (RF) signal and split the RF signal into afirst portion and a second portion, a Doherty amplifier circuitincluding a carrier amplification path coupled to the input circuit toreceive the first portion and a peaking amplification path coupled tothe input circuit to receive the second portion, and an output circuitcoupled to the Doherty amplifier circuit. The output circuit can includea balance to unbalance (BALUN) circuit configured to combine outputs ofthe carrier amplification path and the peaking amplification path toyield an amplified RF signal.

In some embodiments, the PA system can further include a pre-driveramplifier configured to partially amplify the RF signal before receptionby the input circuit. In some embodiments, at least one of the inputcircuit and the output circuit can be implemented as a lumped-elementcircuit.

In some embodiments, the carrier amplification path can include acarrier amplifier and the peaking amplification path can include apeaking amplifier, each of the carrier amplifier and the peakingamplifier including a driver stage and an output stage. In someembodiments, the input circuit can include a modified Wilkinson powerdivider configured to provide DC power to each of the carrier amplifierand the peaking amplifier. In some embodiments, the DC power can beprovided to the carrier amplifier and the peaking amplifier through achoke inductance. In some embodiments, each of the carrier amplificationpath and the peaking amplification path includes a DC blockingcapacitance. In some embodiments, the modified Wilkinson power dividercan be further configured to provide impedance matching between thedriver stages and the pre-driver amplifier. In some embodiments, each ofthe carrier amplification path and the peaking amplification path caninclude an LC matching circuit having a capacitance along the path andan inductive coupling to ground.

In some embodiments, the modified Wilkinson power divider c can beconfigured to provide a desired phase shifting to compensate or tune foran AM-PM effect associated with the peaking amplifier. In someembodiments, the modified Wilkinson power divider can be furtherconfigured to provide a desired attenuation adjustment at an input ofeither the carrier amplifier or the peaking amplifier to compensate ortune for an AM-AM effect associated with the carrier amplifier and thepeaking amplifier. In some embodiments, the modified Wilkinson powerdivider includes a capacitance that couples a first node along thecarrier amplification path to a ground, and an impedance that couples asecond node along the peaking amplification path to the ground. In someembodiments, the modified Wilkinson power divider can further include anisolation resistance implemented between the first node and the secondnode, the isolation resistance selected to prevent or reduce asource-pulling effect between the carrier amplification path and thepeaking amplification path.

In some embodiments, the BALUN circuit can include an LC BALUNtransformer. In some embodiments, the peaking amplifier can beconfigured to behave as a short circuit or a low impedance node when inan off state, and the carrier amplifier can be configured to behave as asingle-ended amplifier equivalent to that of a single-section matchingnetwork having a series inductance and a shunt capacitance whenutilizing the LC BALUN transformer. In some embodiments, the LC BALUNtransformer can be configured such that an impedance seen by the carrieramplifier is increased when in a low power mode. In some embodiments,the impedance seen by the carrier amplifier is approximately doubledwhen in the low power mode.

In some embodiments, the peaking amplifier can be further configured tooperate in a similar manner as a push-pull amplifier where an RF currentfrom the carrier amplifier is influenced by an RF current from thepeaking amplifier. In some embodiments, the push-pull operation canreduce even-harmonics thereby improving linearity.

In some embodiments, the LC BALUN transformer can include a first paththat couples an output of the carrier amplifier to an output node, and asecond path that couples an output of the peaking amplifier to theoutput node. In some embodiments, each of the first path and the secondpath can be inductively coupled to a DC port to provide a DC feed to theoutput stage. In some embodiments, each of the first path and the secondpath can include a harmonic trap. In some embodiments, the harmonic trapcan include a second harmonic trap having an LC shunt to ground and aseries inductance. In some embodiments, the second path can include ashunt capacitance and a series capacitance configured to provide phasecompensation for the output of the peaking amplifier. In someembodiments, at least one of the shunt capacitance and the seriescapacitance can be a surface-mount technology (SMT) capacitor.

In some embodiments, the LC BALUN transformer can be configured toprovide reduced loss in the carrier amplification path to maintain highefficiency at back-off and in a high power mode.

In some embodiments, load modulation of the peaking amplifier can beconfigured such that an impedance loci for the peaking amplifier runfrom an approximately short circuit when the peaking amplifier is in anoff state to an optimum load impedance when the peaking amplifier iscontributing approximately same power as the carrier amplifier.

In some embodiments, the input circuit can be a broadband circuit atleast in part due to a lead-lag network configured to provide broadbandphase shift.

In some embodiments, the input circuit is configured to provide reactiveto real impedance matching, and isolation between the carrier amplifierand peaking amplifier, while providing broadband performance.

In some implementations, the present disclosure relates to a method foramplifying a radio-frequency (RF) signal, the method including providinga Doherty amplifier circuit having a carrier amplification path and apeaking amplification path, receiving an RF signal, splitting the RFsignal into a first portion and a second portion, the first portionprovided to the carrier amplification path, the second portion providedto the peaking amplification path, and combining, using a balance tounbalance (BALUN) circuit, outputs of the carrier amplification path andthe peaking amplification path to yield an amplified RF signal.

In some implementations, the present disclosure relates to a poweramplifier module. The power amplification module can include a packagingsubstrate configured to receive a plurality of components and a poweramplifier (PA) system implemented on the packaging substrate. The PAsystem can include an input circuit configured to receive the RF signaland split the RF signal into a first portion and a second portion. ThePA system can further include a Doherty amplifier circuit having acarrier amplification path coupled to the input to receive the firstportion and a peaking amplification path coupled to the input circuit toreceive the second portion. The PA system can further include an outputcircuit coupled to the Doherty amplifier circuit. The output circuit caninclude a balance to unbalance (BALUN) circuit configured to combineoutputs of the carrier amplification path and the peaking amplificationpath to yield an amplified RF signal. The power amplification module canfurther include a plurality of connectors configured to provideelectrical connections between the PA system and the packagingsubstrate.

In some implementations, the present disclosure relates to a wirelessdevice including a transceiver configured to generate a radio-frequencysignal, a power amplification (PA) module in communication with thetransceiver, and an antenna in communication with the PA module, theantenna configured to facilitate transmission of the amplified RFsignal. The PA module can include an input circuit configured to receivethe RF signal and split the RF signal into a first portion and a secondportion. The PA module can further include a Doherty amplifier circuithaving a carrier amplification path coupled to the input circuit toreceive the first portion and a peaking amplification path coupled tothe input circuit to receive the second portion. The PA module canfurther include an output circuit coupled to the Doherty amplifiercircuit. The output circuit can include a balance to unbalance (BALUN)circuit configured to combine outputs of the carrier amplification pathand the peaking amplification path to yield an amplified RF signal. Thetransceiver can further include an antenna, in communication with the PAmodule, configured to facilitate transmission of the amplified RFsignal.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

The present disclosure relates to U.S. patent application Ser. No.______ [Attorney Docket 75900-50079US], entitled SYSTEMS AND METHODSRELATED TO LINEAR LOAD MODULATED POWER AMPLIFIERS, and U.S. patentapplication Ser. No. ______ [Attorney Docket 75900-50115US], entitledCIRCUITS, DEVICES AND METHODS RELATED TO COMBINERS FOR DOHERTY POWERAMPLIFIERS, filed on even date herewith and hereby incorporated byreference herein in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows that in some embodiments, a power amplifier can beimplemented as a linear and efficient broadband power amplifier.

FIG. 2 shows an example architecture of a power amplifier including acarrier amplification path and a peaking amplification path.

FIG. 3 shows an example configuration of a modified Wilkinson-type powerdivider.

FIG. 4 shows an example configuration of a combiner that can providebalance to unbalance (BALUN) transformer functionality.

FIG. 5 shows first example load modulation profiles of a carrieramplifiers and peaking amplifier using a BALUN transformerconfiguration.

FIG. 6 shows second example load modulation profiles of a carrieramplifiers and peaking amplifier using a BALUN transformerconfiguration.

FIG. 7 shows an example configuration of a power amplifier including amodified Wilkinson-type power divider.

FIG. 8 shows an example broadband phase shift response.

FIG. 9 shows example impedance responses including harmonic traps.

FIG. 10 shows example adjacent channel leakage-power ratio (ACLR) curvesand power-added efficiency (PAE) curves.

FIG. 11 depicts a wireless device having one or more features describedherein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

Described herein are systems, devices, circuits and methods related toradio-frequency (RF) power amplifiers (PAs). FIG. 1 shows that in someembodiments, a PA 100 having one or more features as described hereincan be configured to provide broadband capability with either or both ofdesirable linearity and efficiency. The PA 100 is shown to receive an RFsignal (RF_IN) and generate an amplified signal (RF_OUT). Variousexamples related to such a PA are described herein in greater detail.

FIG. 2 shows an example architecture of a PA 100 having one or morefeatures as described herein. The architecture shown is a Doherty PAarchitecture. Although the various examples are described in the contextof such a Doherty PA architecture, it will be understood that one ormore features of the present disclosure can also be implemented in othertypes of PA systems.

The example PA 100 is shown to include an input port (RF_IN) forreceiving an RF signal to be amplified. Such an input RF signal can bepartially amplified by a pre-driver amplifier 102 before being dividedinto a carrier amplification path 110 and a peaking amplification path130. Such a division can be achieved by a divider 104. Examples relatedto the divider 104 are described herein in greater detail, includingexamples in reference to FIGS. 3 and 7.

In FIG. 2, the carrier amplification path 110 is shown to include anattenuator 112 and amplification stages collectively indicated as 114.The amplification stages 114 are shown to include a driver stage 116 andan output stage 120. The driver stage 116 is shown to be biased by abias circuit 118, and the output stage 120 is shown to be biased by abias circuit 122. In some embodiments, there may be more or less numberof amplification stages. In various examples described herein, theamplification stages 114 are sometimes described as an amplifier;however, it will be understood that such an amplifier can include one ormore stages.

In FIG. 2, the peaking amplification path 130 is shown to include phaseshifting circuit 132 and amplification stages collectively indicated as134. The amplification stages 134 are shown to include a driver stage136 and an output stage 140. The driver stage 136 is shown to be biasedby a bias circuit 138, and the output stage 140 is shown to be biased bya bias circuit 142. In some embodiments, there may be more or lessnumber of amplification stages. In various examples described herein,the amplification stages 134 are sometimes described as an amplifier;however, it will be understood that such an amplifier can include one ormore stages.

FIG. 2 further shows that the carrier amplification path 110 and thepeaking amplification path 130 can be combined by a combiner 144 so asto yield an amplified RF signal at an output port (RF_OUT). Examplesrelated to the combiner 144 are described herein in greater detail,including examples in reference to FIGS. 4 and 7.

In some embodiments, the divider 104 of FIG. 2 can be implemented as alumped-element power splitter. Such a power splitter can be implementedas a modified Wilkinson-type power divider configured to provide DCpower to each of the driver stages (e.g., 116, 136 in FIG. 2). FIG. 3shows an example configuration of a modified Wilkinson-type powerdivider 104 that can be implemented as the divider 104 of FIG. 2. FIG. 7shows an example of how the modified Wilkinson-type power divider 104can be implemented in a circuit example of the PA 100 of FIG. 2.

In FIG. 3, the modified power divider 104 is shown to include an inputport 150 configured to receive an input RF signal. As shown in theexample PA circuit 100 of FIG. 7, the input port 150 can be coupled to acollector of a transistor Q0 of a pre-driver amplifier 102. The inputport 150 is further shown to be coupled to a splitter node 156 throughnode 152. The node 152 is shown to be coupled to a DC supply port 154through an inductance L1 (e.g., an inductor). The DC power for each ofthe driver stages can be obtained through the DC supply port 154. InFIG. 3, L1 can be part of the modified Wilkinson-type splitter whichmatches the impedance looking into the splitter to the impedancepresented to the pre-driver PA collector. At the same time, L1 can serveas a DC path for the pre-driver.

In FIG. 3, the carrier amplification path (110 in FIG. 2) is shown toinclude a path from the splitter node 156 to node 160, through acapacitance C1, node 158, and a capacitance C3. The node 160 may or maynot be connected to a port 162 to facilitate coupling of the foregoingpath to a carrier amplifier (e.g., 114 in FIG. 2). The node 158 is shownto be coupled to ground through a capacitance C2. The node 160 is shownto be coupled to ground through an inductance L2.

In FIG. 3, the peaking amplification path (130 in FIG. 2) is shown toinclude a path from the splitter node 156 to node 166, through acapacitance C4, node 164, and a capacitance C5. The node 166 may or maynot be connected to a port 168 to facilitate coupling of the foregoingpath to a peaking amplifier (e.g., 134 in FIG. 2). The node 164 is shownto be coupled to ground through an inductance L3. The node 166 is shownto be coupled to ground through an inductance L4.

In FIG. 3, a resistance R1 is shown to couple the node 158 of thecarrier amplification path and the node 164 of the peaking amplificationpath. The resistance R1 can be selected to function as an isolationresistor to prevent or reduce source-pulling effect(s) from the carrierand/or peaking amplifiers.

In FIG. 3, the capacitance C1 can be selected to provide DC blockingfunctionality for the carrier amplification path. Similarly, thecapacitance C4 can be selected provide DC blocking functionality for thepeaking amplification path.

In FIG. 3, the capacitance C3 and the inductance L2 can be selected toprovide impedance matching between the pre-driver amplifier (e.g., 102in FIGS. 2 and 7) and the carrier amplifier 114. Similarly, the C5 andthe inductance L4 can be selected to provide impedance matching betweenthe pre-driver amplifier (e.g., 102 in FIGS. 2 and 7) and the peakingamplifier 134.

In FIG. 3, the capacitance C2 associated with the carrier amplificationpath and the inductance L3 associated with the peaking amplificationpath can be selected to provide a desired phase shifting between the twopaths. Such a phase shift can be selected to, for example, compensatefor and/or tune AM-PM phenomena associated with the peaking amplifier134. In FIG. 2, such a phase-shifting functionality is depicted as block132 along the peaking amplification path 130.

In some embodiments, and as shown in FIG. 2, an attenuator 112 can beprovided along either the carrier amplification path 110 (e.g., beforethe carrier amplifier 114) or the peaking amplification path 130 (e.g.,before the peaking amplifier 134). Such an attenuator can be configuredto provide a desired attenuation adjustment to compensate for and/ortune AM-AM phenomena associated with either or both of the carrier andpeaking amplifiers. Such an attenuator can also promote uneven powersplitting between the two amplification paths.

It is noted that the foregoing corrections and/or tuning of the AM-AMand/or AM-PM effects can result in the PA 100 of FIGS. 2 and 7 to besubstantially linear. Such linearity can be achieved without requiringdigital pre-distortion which typically reduces efficiency of the PAsystem and applicability of the PA system in amplifiers for portablewireless devices. Further, linearity achieved by the PA 100 of FIGS. 2and 7 (without the digital pre-distortion) can be similar to linearityperformance associated with a class-AB single-ended amplifier.

In some embodiments, the combiner 144 of FIG. 2 can be implemented as orsimilar to a lumped-element balanced to unbalanced (BALUN) transformer.FIG. 4 shows an example configuration of a combiner 144 that can providesuch BALUN transformer functionality. FIG. 7 shows an example of how thecombiner 144 can be implemented in a circuit example of the PA 100 ofFIG. 2.

In FIG. 4, the combiner 144 is shown to include a portion of the carrieramplification path (e.g., 110 in FIG. 2) and a portion of the peakingamplification path (130) joined at a combining node 186. The combiningnode 186 is shown to be coupled to an output port 198 (RF_OUT in FIGS. 2and 7).

In FIG. 4, the portion of the carrier amplification path is shown tocouple the combining node 186 and node 182 through an inductance L13.The node 182 may or may not be connected to a port 180 to facilitatecoupling of the foregoing path to a carrier amplifier (e.g., 114 in FIG.2). The node 182 is shown to be coupled to ground through a capacitanceC11 and an inductance L12. The node 182 is also shown to be coupled to aport 184 through an inductance L11.

In FIG. 4, the portion of the peaking amplification path is shown tocouple the combining node 186 and node 192 through an inductance L16,node 196, and a capacitance C14. The node 192 may or may not beconnected to a port 190 to facilitate coupling of the foregoing path toa peaking amplifier (e.g., 134 in FIG. 2). The node 192 is shown to becoupled to ground through a capacitance C12 and an inductance L15. Thenode 192 is also shown to be coupled to a port 194 through an inductanceL14. The node 196 is shown to be coupled to ground through a capacitanceC13.

In FIG. 4, the node 182 can be coupled to the collector of the outputstage (e.g., 120 in FIG. 2) of the carrier amplifier (114) through theport 180. Accordingly, DC feed can be provided to the output stage (120)of the carrier amplifier (114) through the port 184 and the inductanceL11. Similarly, the node 192 can be coupled to the collector of theoutput stage (e.g., 140 in FIG. 2) of the peaking amplifier (134)through the port 190. Accordingly, DC feed can be provided to the outputstage (140) of the peaking amplifier (134) through the port 194 and theinductance L14.

In FIG. 4, the capacitance C11, the inductance L12, and the inductanceL13 can be selected to function as a second harmonic trap for the outputof the carrier amplifier (114). Similarly, the capacitance C12, theinductance L15, and the inductance L16 can be selected to function as asecond harmonic trap for the output of the peaking amplifier (134).

In FIG. 4, the capacitance C13 and the capacitance C14 can be selectedto provide phase compensation for the output of the peaking amplifier(134). In some embodiments, C13 and C14 can be implemented assurface-mount technology (SMT) capacitors. In such embodiments, using aslittle as two SMT capacitors, the combiner 144 can be implemented as abroadband power combiner.

The example combiner 144 of FIG. 4 can provide desirable functionalitiesfor operations of Doherty PA architectures. For example, the peakingamplifier in a Doherty PA architecture is typically required to behaveas a short circuit or a very low impedance path when it is turned off,and the carrier amplifier typically acts as a single-ended amplifierwith an equivalent circuit that is similar to or the same as a typicalsingle-section matching network (e.g., series L and shunt C) when usingan LC BALUN configuration. In such a state, impedance seen by thecarrier amplifier can be doubled.

When the peaking amplifier is turned on, the PA system can operate in amanner similar to a “push-pull” amplifier. For example, the RF currentfrom the carrier amplifier can see the current from the peakingamplifier. In such a state, linearity can be improved since the evenharmonic content can be reduced.

As described herein, the combiner 144 with the example LC BALUNconfiguration can be implemented in a compact form, using as little astwo SMT components (e.g., capacitors). Such a combiner can be configuredto provide impedance matching from, for example, a 50-Ohm output totransistor-collectors of the peaking and carrier amplifiers, includingRF chokes and harmonic traps.

As described herein, the combiner 144 with the example LC BALUNconfiguration can be implemented to reduce the loss in the carrieramplifier path compared to other Doherty topologies. Such a feature inturn can facilitate maintenance of high efficiency at back-off and highpower modes. Further, the LC BALUN configuration can provide required ordesired impedance and phase adjustment for the carrier amplifier. Such afeature can be important when designing an asymmetric loaded Dohertytransmitter.

In some embodiments, load modulation associated with a peaking amplifieras described herein is generally opposite as in conventional Dohertytransmitters. FIG. 5 shows load modulation profiles for carrier (200)and peaking (202) amplifiers of a conventional Doherty transmitter usinga BALUN transformer configuration. FIG. 6 shows load modulation profilesfor carrier (204) and peaking (206) amplifiers of a Doherty transmitterusing a BALUN transformer configuration as described herein (e.g., FIG.7). For the peaking amplifiers in FIGS. 5 and 6, one can see thatimpedance loci run in opposite directions from their respective shortcircuit states (e.g., when the peaking amplifier is turned off) to theirrespective optimum load impedance conditions (e.g., when the peakingamplifier is contributing same power as the carrier amplifier). For theconventional example of FIG. 5, the impedance loci of the peakingamplifier run in the same direction as that of the carrier amplifier aspower is increased. For the example of FIG. 6, the impedance loci of thepeaking amplifier run in the opposite direction as that of the carrieramplifier as power is increased.

FIG. 7 shows an example of a PA 100 having one or more features asdescribed herein. The PA can include a pre-driver amplifier 102 such asa one-stage single-ended amplifier. The output of the pre-driveramplifier 102 is shown to be provided to a divider 104, such as theexample described in reference to FIG. 3. The divided outputs of thedivider 104 are shown to be provided to a carrier amplifier 114 and apeaking amplifier 134. The outputs of the carrier amplifier 114 and thepeaking amplifier 134 are shown to be combined by a combiner 144, suchas the example described in reference to FIG. 4.

In the example PA 100 of FIG. 7, the divider 104 and the combiner 144can yield a broadband combination. For example, the divider 104 isbroadband in nature due to, for example, the lead-lag network thatprovides broadband phase shift. An example of such a phase shiftresponse is shown as curve 250 in FIG. 8. The example response curve 250is representative of a typical phase difference between the matchingreactive base impedances and the driver amplifier collector. It isfurther noted that the divider 104 provides advantageous features suchas reactive to real impedance matching, isolation between carrier andpeaking amplifiers, and still yield broadband performance.

In another example, the combiner 144 with its LC BALUN configuration canalso contribute to the broadband performance of the PA 100. As describedherein, the LC BALUN can include harmonic traps configured to keep theimpedance locus within lower constant Q circles. Example of suchimpedance responses are shown as curves 260, 262, 264 in FIG. 9. Theexample response curves 260, 262, 264 are representative of collectorload impedance vs. frequency for different ZP values. ZP1 represents theload impedance seen by carrier PA collector when both carrier andpeaking PAs are turned on (in operation) and it is about 5.7+j0.119 Ohmsin the example. ZP2 is the collector impedance at the peaking PAcollector which is similar to the previous case (e.g., same impedancewhen both PAs are on). ZP4 is the impedance seen by carrier PA collectorwhen peaking PA is off which is effectively doubled to around10.86+j0.058 Ohms in the example. Such a feature effectively enhancesthe PA architecture bandwidth, since the impedances vs. frequency arenot spread along the Smith chart.

A PA architecture having one or more features as described herein,including the examples of FIGS. 1-4 and 7, can be configured to yieldexcellent linear and efficient broadband performance. For example, a 21%relative bandwidth can be achieved for −37-dBc ACLR (adjacent channelleakage-power ratio) using an LTE signal (e.g., 10-MHz BW, QPSK, 12 RB).FIG. 10 shows ACLR curves and power-added efficiency (PAE) curves fordifferent samples. The upper set of curves (270, 292) are for poweradded efficiency (PAE) for 27.5 and 27 dBm output power levels,respectively. The middle set of curves (274, 276) are for ACLR1 for 27.5and 27 dBm output power levels, respectively. The dashed curve (278) isfor ACLR2 for 27.5 dBm output power. In the context of ACLR performance,one can see that the −37-dBc ACLR bandwidth at 27-dBm output power isapproximately 525 MHz (e.g., between markers “m39” and “m38”) which isapproximately 21% of the center frequency of approximately 2,500 MHz(e.g., marker “m48). It is noted that bandwidth can be even wider if theACLR level is allowed to increase.

In some implementations, a device and/or a circuit having one or morefeatures described herein can be included in an RF device such as awireless device. Such a device and/or a circuit can be implementeddirectly in the wireless device, in a modular form as described herein,or in some combination thereof. In some embodiments, such a wirelessdevice can include, for example, a cellular phone, a smart-phone, ahand-held wireless device with or without phone functionality, awireless tablet, etc.

FIG. 11 schematically depicts an example wireless device 400 having oneor more advantageous features described herein. In the example, one ormore PAs 110 collectively indicated as a PA architecture 100 can includeone or more features as described herein. Such PAs can facilitate, forexample, multi-band operation of the wireless device 400.

The PAs 110 can receive their respective RF signals from a transceiver410 that can be configured and operated to generate RF signals to beamplified and transmitted, and to process received signals. Thetransceiver 410 is shown to interact with a baseband sub-system 408 thatis configured to provide conversion between data and/or voice signalssuitable for a user and RF signals suitable for the transceiver 410. Thetransceiver 410 is also shown to be connected to a power managementcomponent 406 that is configured to manage power for the operation ofthe wireless device 400. Such power management can also controloperations of the baseband sub-system 408 and the Pas 110.

The baseband sub-system 408 is shown to be connected to a user interface402 to facilitate various input and output of voice and/or data providedto and received from the user. The baseband sub-system 408 can also beconnected to a memory 404 that is configured to store data and/orinstructions to facilitate the operation of the wireless device 400,and/or to provide storage of information for the user.

In the example wireless device 400, outputs of the PAs 110 are shown tobe matched (via match circuits 420) and routed to an antenna 416 viatheir respective duplexers 412 a-412 d and a band-selection switch 414.The band-selection switch 414 can be configured to allow selection of anoperating band. In some embodiments, each duplexer 412 can allowtransmit and receive operations to be performed simultaneously using acommon antenna (e.g., 416). In FIG. 11, received signals are shown to berouted to “Rx” paths (not shown) that can include, for example, alow-noise amplifier (LNA).

A number of other wireless device configurations can utilize one or morefeatures described herein. For example, a wireless device does not needto be a multi-band device. In another example, a wireless device caninclude additional antennas such as diversity antenna, and additionalconnectivity features such as Wi-Fi, Bluetooth, and GPS.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Description using the singularor plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While some embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A power amplifier (PA) system comprising: aninput circuit configured to receive a radio-frequency (RF) signal andsplit the RF signal into a first portion and a second portion; a Dohertyamplifier circuit including a carrier amplification path coupled to theinput circuit to receive the first portion and a peaking amplificationpath coupled to the input circuit to receive the second portion; and anoutput circuit coupled to the Doherty amplifier circuit, the outputcircuit including a balance to unbalance (BALUN) circuit configured tocombine outputs of the carrier amplification path and the peakingamplification path to yield an amplified RF signal.
 2. The PA system ofclaim 1 further comprising a pre-driver amplifier configured topartially amplify the RF signal before reception by the input circuit.3. The PA system of claim 2 wherein the carrier amplification pathincludes a carrier amplifier and the peaking amplification path includesa peaking amplifier, each of the carrier amplifier and the peakingamplifier including a driver stage and an output stage.
 4. The PA systemof claim 3 wherein the input circuit includes a modified Wilkinson powerdivider configured to provide DC power to each of the carrier amplifierand the peaking amplifier.
 5. The PA system of claim 4 wherein themodified Wilkinson power divider is further configured to provideimpedance matching between the driver stages and the pre-driveramplifier.
 6. The PA system of claim 3 wherein the modified Wilkinsonpower divider is further configured to provide a desired phase shiftingto compensate or tune for an AM-PM effect associated with the peakingamplifier.
 7. The PA system of claim 3 wherein the modified Wilkinsonpower divider is further configured to provide a desired attenuationadjustment at an input of either the carrier amplifier or the peakingamplifier to compensate or tune for an AM-AM effect associated with thecarrier amplifier and the peaking amplifier.
 8. The PA system of claim 7wherein the modified Wilkinson power divider includes a capacitance thatcouples a first node along the carrier amplification path to a ground,and an impedance that couples a second node along the peakingamplification path to the ground.
 9. The PA system of claim 8 whereinthe modified Wilkinson power divider further includes an isolationresistance implemented between the first node and the second node, theisolation resistance selected to prevent or reduce a source-pullingeffect between the carrier amplification path and the peakingamplification path.
 10. The PA system of claim 3 wherein the BALUNcircuit includes an LC BALUN transformer.
 11. The PA system of claim 10wherein the peaking amplifier is configured to behave as a short circuitor a low impedance node when in an off state, and the carrier amplifieris configured to behave as a single-ended amplifier equivalent to thatof a single-section matching network having a series inductance and ashunt capacitance when utilizing the LC BALUN transformer.
 12. The PAsystem of claim 11 wherein the LC BALUN transformer is configured suchthat an impedance seen by the carrier amplifier is increased when in alow power mode.
 13. The PA system of claim 12 wherein the impedance seenby the carrier amplifier is approximately doubled when in the low powermode.
 14. The PA system of claim 11 wherein the peaking amplifier isfurther configured to operate in a similar manner as a push-pullamplifier where an RF current from the carrier amplifier is influencedby an RF current from the peaking amplifier.
 15. The PA system of claim14 wherein the push-pull operation reduces even-harmonics therebyimproving linearity.
 16. The PA system of claim 3 wherein each of afirst path that couples an output of the carrier amplifier to an outputnode and a second path that couples an output of the peaking amplifierto an output node includes a harmonic trap.
 17. The PA system of claim16 wherein the harmonic trap includes a second harmonic trap having anLC shunt to ground and a series inductance.
 18. The PA system of claim 3wherein load modulation of the peaking amplifier is configured such thatan impedance loci for the peaking amplifier run from an approximatelyshort circuit when the peaking amplifier is in an off state to anoptimum load impedance when the peaking amplifier is contributingapproximately same power as the carrier amplifier.
 19. A power amplifiermodule comprising: a packaging substrate configured to receive aplurality of components; a power amplifier (PA) system implemented onthe packaging substrate, the PA system including an input circuitconfigured to receive the RF signal and split the RF signal into a firstportion and a second portion, the PA system further including a Dohertyamplifier circuit having a carrier amplification path coupled to theinput circuit to receive the first portion and a peaking amplificationpath coupled to the input circuit to receive the second, the PA systemfurther including an output circuit coupled to the Doherty amplifiercircuit, the output circuit including a balance to unbalance (BALUN)circuit configured to combine outputs of the carrier amplification pathand the peaking amplification path to yield an amplified RF signal; anda plurality of connectors configured to provide electrical connectionsbetween the PA system and the packaging substrate.
 20. A wireless devicecomprising: a transceiver configured to generate a radio-frequency (RF)signal; a power amplifier (PA) module in communication with thetransceiver, the PA module including an input circuit configured toreceive the RF signal and split the RF signal into a first portion and asecond portion, the PA module further including a Doherty amplifiercircuit having a carrier amplification path coupled to the input circuitto receive the first portion and a peaking amplification path coupled tothe input circuit to receive the second portion, the PA module furtherincluding an output circuit coupled to the Doherty amplifier circuit,the output circuit including a balance to unbalance (BALUN) circuitconfigured to combine outputs of the carrier amplification path and thepeaking amplification path to yield an amplified RF signal; and anantenna in communication with the PA module, the antenna configured tofacilitate transmission of the amplified RF signal.